1. Technical Field
The present principles generally relate to improving the quality of voice and data communication traffic and, more particularly, to improving the quality of voice and data communication traffic over a wireless multi-hop network.
2. Description of the Related Art
Most traffic transmitted over the internet employs a Transmission Control Protocol (TCP), which was originally designed for wired networks. A common means for providing internet access includes utilizing a wireless multi-hop network as an extension of a wired network or as a bridge between wired networks. FIG. 1A provides an example of a wireless multi-hop network 102 employed as a bridge between wired networks 114 and 116 through gateways 104 and 106, respectively. As illustrated in FIG. 1A, a wireless multi-hop network may be comprised of wireless nodes 108 that may act as transceivers through which a stream of TCP packets 118 may be transmitted between a client 110 in wired network 114 and a client 112 in wired network 116.
Unfortunately, TCP utilization in a dual wired/wireless multi-hop network configuration has a tendency to exhibit severe degradation of communication traffic. TCP was originally designed to provide reliable end-to-end delivery of data over unreliable networks. As discussed herein below, TCP has been carefully optimized in the context of wired networks with rules and protocols that are unsuitable for wireless multi-hop networks.
Another type of traffic that has recently become more prevalent in homes and institutions is Voice Internet Protocol (VoIP) traffic. VoIP capability is currently available in many cellular telephones as well, due to the convenience and cost savings it provides. VoIP, however, is different from most other traffic in that it has relatively stringent delivery requirements. While mechanisms for providing a quality of service (QoS) required by VoIP traffic have been developed for wired networks, current communication protocols do not sufficiently ensure that quality of service requirements of VoIP traffic over wireless networks are met. Rather, a large amount of research has focused on the optimization of the TCP performance over wireless networks. The majority of the solutions proposed by the research community fall in four main categories: connection splitting solutions, link layer solutions, client modification solutions and gateway solutions.
Connection Splitting Solutions
With continuing reference to FIG. 1A, key problems with using TCP over hybrid wireless/wired networks stem from the different characteristics of wireless networks and wired networks, such as the Internet. While most packet losses in wireless networks are due to hidden terminals and channel contention at the intermediate nodes, drops in the Internet or other wired network are almost always due to buffer overflows at the routers. One known solution to this network convergence problem involves splitting the TCP connection at an interface node between the wired and wireless portions of the network. The interface may be referred to as an internet gateway. Elements 104 and 106 of FIG. 1A are examples of internet gateways.
In accordance with connection splitting solutions, a TCP connection may be divided into three separate connections: (1) the connection between TCP client A 110 and edge router 104, (2) the connection between edge routers 104 and 106, and (3) the connection between edge router 106 and TCP client B 112. Data sent to the TCP client B 112 from TCP client A 110 is first received by the edge router 104. Thereafter, an acknowledgement is sent by the edge router 104 to the TCP client A 110 and data is forwarded to edge router 106 at the other side. Subsequently, the data is transferred to the TCP client B 112.
Connection splitting can hide the wireless link entirely by terminating the TCP connection prior to the wireless link at the base station or access point 104, 106. With this approach, the communication in wireless network 102 may be optimized independently of the TCP applications. However, connection splitting entails employing additional overhead to maintain two connections for one TCP communication session. The dual stack at the edge-router is required to keep track of all of the TCP connections. Connection splitting also violates end-to-end TCP semantics, which increases vulnerability to failure of proxies at an edge router because an acknowledgement to a sender is no longer a true indication that a receiver has received a data packet. Furthermore, connection splitting complicates the handover process.
Link Layer Solutions
Link layer solutions attempt to make the wireless link layer appear as a wired layer from the perspective of TCP senders and receivers. One such proposal is a snoop protocol. Here, a snoop agent is introduced at a base station to perform local retransmissions using information sniffed from the TCP traffic passing through the base station. Another link layer solution proposes QoS scheduling with priority queues in an access point (AP) to improve VoIP quality by placing TCP data in a lower QoS level.
Client Modification Solutions
With reference to FIG. 1B, a modified-client system 150 for improving TCP performance over a wireless network 160 is illustrated. A common client modification solution improves TCP performance by configuring TCP senders, such as modified TCP clients 152 and 154, to obtain knowledge of the wireless network with feedback information from the network of wireless nodes 162. However, because the solution relies on modification of existing TCP applications, it causes an interoperability problem with existing TCP applications such that communication with existing applications may be hindered. As a result, the solution has limited applicability.
Gateway Solutions
Gateway solutions address TCP performance problems over wireless networks by evenly spacing, or pacing, data sent into a multi-hop network over an entire round-trip time, so that data is not sent in a burst. Pacing may be implemented using a data and/or acknowledgement (ACK) pacing mechanism. For example, TCP-Gateway Adaptive Pacing (TCP-GAP) is a congestion control scheme that reduces bursts of TCP packets based on estimating 4-hop propagation delay and variance of recent round trip delay times (RTT) at an Internet gateway for wired-wireless hybrid networks. The TCP-GAP scheme is relatively responsive, provides fairness among multiple TCP flows and also provides better goodput than TCP-New Reno, which is another TCP-variant. However, TCP-GAP depends on network topology and fails to estimate TCP bandwidth accurately in the presence of real-time traffic, such as VoIP. In addition, congestion control is performed in accordance with the general TCP scheme, which tends to be too aggressive for wireless multi-hops.
While known TCP variants may improve TCP data transmission over wireless multi-hop networks, they fail to adequately provide or maintain a sufficient quality of VoIP traffic over wireless multi-hop networks through which TCP data is transmitted. In addition, even priority schemes, including priority built into a media access control layer such as Request to Send/Clear to Send (RTS/CTS) or 802.11e mechanisms, generally cannot protect voice traffic. Accordingly, there is a need for methods and systems for providing or maintaining a sufficient VoIP traffic quality while efficiently utilizing the remaining transmission capacity for data traffic.